Electronic device manufacturers strive to produce a rich interface for users. Many devices use visual and auditory cues to provide feedback to a user. In some interface devices, a kinesthetic effect (such as active and resistive force feedback) and/or a tactile effect (such as a vibration) are also provided to the user. Kinesthetic effects and tactile effects may more generally be referred to as “haptic feedback” or “haptic effects”. Haptic feedback can provide cues that enhance and simplify the user interface. For example, vibration effects, or vibrotactile haptic effects, may be useful in providing cues to users of electronic devices to alert the user to specific events, or provide realistic feedback to create greater sensory immersion within a simulated or virtual environment.
To generate a haptic effect, many devices use an actuator. Example actuators for generating a haptic effect (also referred to as a haptic actuator) include an eccentric rotating mass (“ERM”) actuator, in which an eccentric mass is moved by a motor, and a linear resonant actuator (“LRA”), in which a mass attached to a spring is driven back and forth. Other actuators include actuators that use a “smart material,” such as a piezoelectric material, an electro-active polymer, or a shape memory alloy. In order to generate a haptic effect, a driving signal may be applied to a haptic actuator.